In the manufacture of containers such as glass bottles and jars, various types of anomalies can occur in the sidewalls, heels, bottoms, shoulders, necks and finishes of the containers. These anomalies, termed "commercial variations" in the art, can affect commercial acceptability of the containers. It has been proposed to employ electro-optical inspection techniques for detecting commercial variations that affect the optical properties of the containers. The basic principle is that a light source is positioned to direct light energy onto a container, and a camera is positioned to receive light energy after interaction with the portion(s) of the container illuminated by the light source. Commercial variations in the portion of the container illuminated by the light source are detected as a function of the intensity of the light energy incident on the sensor. Detection of commercial variations in a container can result in rejection of the container, depending upon the type of variation. For example, checks, which are mirror-like cracks in a container sidewall or finish, can result in stress concentration and failure of a container, and thus would normally automatically result in container rejection regardless of size or position. On the other hand, blisters in a container finish can be acceptable if sufficiently small in size.
In the art of container manufacture, the term "container finish" generally refers to that portion of the container that defines the container mouth. In a bottle, for example, the finish includes that portion of the container neck having threads and/or beads for receiving the container cap, as well as the upper surface of the neck surrounding the container mouth, termed the "sealing surface," against which the cap seats.
U.S. Pat. No. 4,378,493, assigned to the assignee of the present application, discloses an apparatus and method for inspecting containers, in which glass containers are conveyed in sequence through a plurality of stations where they are physically and optically inspected. Differing mechanical and electro-optical inspections are performed at the sequential stations, typically one inspection per station. The number of inspections that can be performed is thus limited by the number of stations in the apparatus.
U.S. Pat. No. 5,200,801, also assigned to the assignee of the present application, discloses a method and apparatus that can be implemented at one of the inspection stations for detecting vertical checks in the finish of a translucent container. A light source directs light energy onto the container finish from externally of the container finish laterally of the container axis over an angular portion less than the entire circumference of the container finish. An area array camera is positioned externally of the container at an angle to the container axis to receive an image of the illuminated portion of the container finish. The camera is oriented with respect to the light source such that a vertical check in the container finish reflects light energy from the source to the camera to create a bright image of the check against a normally dark background. Vertical checks in the container finish are detected as a function of such reflected light energy. Use of an area array sensor permits detection of vertical checks over an increased angular range with respect to the radius of the container finish.
It is a general object of the present invention to provide an apparatus and method for detecting checks in the finish of a translucent container in which a container finish may be inspected for both horizontal and vertical checks at a single inspection station, thus improving efficiency of the inspection process. Another object of the present invention is to provide a method and apparatus of the described character that are user friendly, and that can be readily adjusted in the field for inspecting container finishes of differing diameter. Yet another object of the present invention is to provide a method and apparatus of the described character that detect both horizontal and vertical checks over an increased angular range as compared with the prior art. A further object of the invention is to provide a method and apparatus of the described character for detecting checks in the finish of a translucent container that provide improved uniformity of illumination at the container finish inspection area, and that eliminate spherical aberration in the illumination beams.